首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   4309篇
  免费   146篇
  国内免费   10篇
测绘学   178篇
大气科学   601篇
地球物理   999篇
地质学   1742篇
海洋学   192篇
天文学   572篇
综合类   15篇
自然地理   166篇
  2021年   65篇
  2020年   59篇
  2019年   43篇
  2018年   131篇
  2017年   147篇
  2016年   215篇
  2015年   128篇
  2014年   190篇
  2013年   243篇
  2012年   111篇
  2011年   161篇
  2010年   171篇
  2009年   221篇
  2008年   156篇
  2007年   118篇
  2006年   124篇
  2005年   98篇
  2004年   67篇
  2003年   79篇
  2002年   93篇
  2001年   82篇
  2000年   78篇
  1999年   69篇
  1998年   75篇
  1997年   68篇
  1996年   51篇
  1995年   69篇
  1994年   78篇
  1993年   36篇
  1992年   32篇
  1991年   32篇
  1990年   43篇
  1989年   36篇
  1988年   29篇
  1987年   32篇
  1985年   42篇
  1984年   46篇
  1983年   57篇
  1982年   44篇
  1981年   41篇
  1980年   41篇
  1979年   30篇
  1978年   56篇
  1977年   32篇
  1976年   32篇
  1975年   45篇
  1974年   55篇
  1973年   51篇
  1969年   26篇
  1962年   26篇
排序方式: 共有4465条查询结果,搜索用时 15 毫秒
961.
Over the past decade, political framework in the energy sector all over the world has provoked a strong focus on the production of renewable energies. The study focuses on agent-based modelling approach to identify the suitable and economical distribution of biogas power plants over time in the area of interest. For sufficient supply of biomass (silage maize) on a regional basis to run biogas power plants economically and smoothly, different thematic layers with defined rules for Agent Analyst used to simulate the future installations of power plants. In conjunction with ArcGIS, the Agent Analyst software generates simulations that prove the robustness of the model in finding the suitable location of power plants. The resultant location from the model is analysed in different aspects. The designed methodology could be implemented in other areas with minor edits as per requirement of the area.  相似文献   
962.
The exploitation of resources, if not properly managed, can lead to spoiling natural habitats as well as to threatening people’s health, livelihoods and security. The paper discusses a multi-scale Earth observation-based approach to provide independent information related to exploitation activities of natural resources for countries which are experiencing armed conflict. The analyses are based on medium to very high spatial resolution optical satellite data. Object-based image analysis is used for information extraction at these different scales. On a subnational level, conflict-related land cover changes as an indication of potential hot spots for exploitation activities are classified. The regional assessment provides information about potential activity areas of resource exploitation, whereas on a local scale, a site-specific assessment of exploitation areas is performed. The study demonstrates the potential of remote sensing for supporting the monitoring and documentation of natural resource exploitation in conflict regions.  相似文献   
963.
Liu  Xueyuan  Köhl  Armin  Stammer  Detlef  Masuda  Shuhei  Ishikawa  Yoichi  Mochizuki  Takashi 《Climate Dynamics》2017,49(3):1061-1075

We investigated the influence of dynamical in-consistency of initial conditions on the predictive skill of decadal climate predictions. The investigation builds on the fully coupled global model “Coupled GCM for Earth Simulator” (CFES). In two separate experiments, the ocean component of the coupled model is full-field initialized with two different initial fields from either the same coupled model CFES or the GECCO2 Ocean Synthesis while the atmosphere is initialized from CFES in both cases. Differences between both experiments show that higher SST forecast skill is obtained when initializing with coupled data assimilation initial conditions (CIH) instead of those from GECCO2 (GIH), with the most significant difference in skill obtained over the tropical Pacific at lead year one. High predictive skill of SST over the tropical Pacific seen in CIH reflects the good reproduction of El Niño events at lead year one. In contrast, GIH produces additional erroneous El Niño events. The tropical Pacific skill differences between both runs can be rationalized in terms of the zonal momentum balance between the wind stress and pressure gradient force, which characterizes the upper equatorial Pacific. In GIH, the differences between the oceanic and atmospheric state at initial time leads to imbalance between the zonal wind stress and pressure gradient force over the equatorial Pacific, which leads to the additional pseudo El Niño events and explains reduced predictive skill. The balance can be reestablished if anomaly initialization strategy is applied with GECCO2 initial conditions and improved predictive skill in the tropical Pacific is observed at lead year one. However, initializing the coupled model with self-consistent initial conditions leads to the highest skill of climate prediction in the tropical Pacific by preserving the momentum balance between zonal wind stress and pressure gradient force along the equatorial Pacific.

  相似文献   
964.
965.
Through the use of a Monte Carlo type calculation, the lateral dispersion of a fine proton beam of given energy and pitch angle in an atmosphere of given exospheric temperature is investigated. It is found that this lateral dispersion may be estimated by using a simple analytical expression.  相似文献   
966.
J. Köppen 《Solar physics》1975,42(2):325-332
Observations of a sunspot during and after a partial solar eclipse are described. The amount of scattered light confirms the existence of a spread function component with a half width of 10″. The observations also indicate the possibility of severely underestimating this component by aureole measurements. Umbral continuum intensities of 0.10 I in the red spectral region were directly measured, the correction for scattered light amounts to 0.02 I . Intensities calculated with four umbral models are larger than the observed values, indicating this sunspot to be cooler by some 100 K. The wings of two strong Ca i lines are equally explained by the models of Henoux, Kneer, and Stellmacher/Wiehr. Yun's model can be ruled out because of too high a temperature.  相似文献   
967.
Letx 0 (t),x 0 4 be a homothetic solution of the planar three-body problem with total energyh, described in relative coordinates with respect to one body. It is shown that the variational equation of the problem atx 0 (t) can be solved explicitly in terms of hypergeometric functions. This is done by using the scaled true anomaly of the one-dimensional Kepler motion as the independent variable.The classical theorems about hypergeometric functions allow a simple calculation of all the values needed in applications. By means of this theory the past of a homothetic triple close encounter may be described in a linearized approximation.Proceedings of the Sixth Conference on Mathematical Methods in Celestial Mechanics held at Oberwolfach (West Germany) from 14 to 19 August, 1978.  相似文献   
968.
Fourteen coudé spectrograms (eight with dispersion 12.4 Å mm–1 and six 7 Å mm–1) of the Cr star UMa (Ap) have been studied. The observations were made at the Haute Provence Observatory. The radial velocities of the various ions have been measured. The existence of Balmer progression in radial velocity is doubtful. The variability of some lines is in the opposite sense of K of Caii. Both a rough and a fine analysis have been made. The results of these analyses are compared and found to be in good agreement. The results of the fine analysis indicate a defect of Al, Si and Ca; Sc, Ti, Fe and Sr are normal, Mg and Ni are in slight excess. V, Cr and Mn are in excess by factors of 3, 12, 19; Y, Zr and Ba are in excess by factors of 9, 15, 30. Rare earths are in excess by factors ranging between 100–1000. These results are compared with the majority of the Cr–Eu–Sr stars.The observations have been made at the 152 cm coudé telescope of the Haute Provence Observatory.  相似文献   
969.
970.
Summary Types of chemical bonding in magnetite are discussed. Magnetite spinel lattice is characterized by tetrahedral covalent bonds and octahedral electrovalent bonds. The consequences for oxidation processes are studied in connection with hitherto existing experimental and theoretical results.
Zusammenfassung Der Charakter der chemischen Bindung im Magnetit wird diskutiert. Für das Spinellgitter des Magnetits sind tetraedrische kovalente und oktaedrische elektrovalente Bindungen typisch. Die Auswirkungen dieses Bindungszustandes auf den Ablauf der Oxydationsvorgänge wird überprüft an Hand der bisher vorliegenden experimentellen und theoretischen Teilergebnisse.


Dr. Dr. habil.F. Frölich, Dr.H. Stiller, Geomagnetic InstituteFotsdam, German Academy of Science at Berlin, Mitteilung Nr. 133.  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号